Combustible cartridge with fibrous porous base having crystalline explosive disposed therein



United States Patent F 3,504,630 COMBUSTIBLE CARTRIDGE WITH FIBROUS POROUS BASE HAVING CRYSTALLINE EX- PLOSIVE DISPOSED THEREIN Jean Paul Picard, Morristown, N.J., assignor to the United States of America as represented by the Secretary of the Army No Drawing. Filed Mar. 14, 1968, Ser. No. 712,913 Int. Cl. F42b 1/00 US. Cl. 102-43 24 Claims ABSTRACT OF THE DISCLOSURE A combustible cartridge having a fibrous base containing voids wherein are deposited a crystalline explosive which is held in position in relation to the base by electrostatic forces.

A process wherein a fibrous base is dispersed in water and treated with anionic charge-inducing agent. The base is then treated with a binding agent to facilitate forming. Subsequently, a crystalline explosive is added to the dispersion and the item is formed and dried. Prior to the addition of the explosive, it is treated with a cationic charge-inducing agent to facilitate bonding to the fibrous base.

This invention relates to a combustible cartridge or case for use in munitions and a method of making the same.

The cartridge or case, prepared in accordance with this invention, is for use as a container for the high energy ingredients of a munition such as propellants, igniters, and pyrotechnic compositions. Disposable containers for munitions such as cartridges and cases have been prepared in the past. However, these have not possessed all that is desired of such containers in the field. For instance, such containers, cartridges or cases are not completely combustible. Further, lack of strength of such containers leads to many problems in the field as does lack of imperviousness to water and moisture. Also, problems in fabrication and cost have been quite vexing.

US. Patents 2,991,168 and 3,304,867 have dealt with the above problems at length. These patents teach that the combustibility of such cartridges or cases may be somewhat improved through the use of nitrocellulose, either in spun filament or fibrous form, as the basis of construction of the item. However, due to the low thermal stability and the poor physical properties of such material, the problems facing the art have not been adequately solved. For instance, the problem of strength which is a basic requirement of such containers has not been completely solved.

However, to some extent, the strength of such combustible containers, cartridges or cases may be somewhat increased through the use of polymeric binders. But, this technique gravely impairs the combustibility of the item. Also, the low thermal stability of such combustible containers, cartridges and cases may be somewhat improved by the addition of conventional stabilizers. However, their reactions and by-products are known to be deleterious to the physical strength of the item. For instance, in some cases, the deleterious gases given off by such additives have been known to degrade the cellulose molecule and its derivatives leading to the lowering of the overall physical properties of the system.

Further, one of the methods of fabricating a combustible cartridge or case is the felting technique. This requires that a uniform aqueous slurry of cellulose fibers be prepared and felted by suction on a screened forming die. Once the desired thickness is achieved, the formed 3,504,630 Patented Apr. 7, 1970 case is then removed from the die by reverse pressurization with compressed air. The moist case is then lifted from the tank, dried, and dipped in a non-aqueous solution of a lacquer-like solution. After removing the excess lacquer, the case is dried. The difficulties with the technique include the danger of handling dry nitrocellulose. Also, the ultimate physical properties and combustibility of the case depend on the amount of lacquer utilized and its uniform distribution through the dried case.

The subject invention answers the needs of the art with special emphasis on a combustible cartridge or case and method of making the same. The cartridge or case of this invention, which is easily ignitable, possesses improved physical and chemical properties including a controllable burning rate and a more complete degree of combustion. Further, the process of this invention is based entirely upon an aqueous system which leads to a more uniform dispersion of binder and a more complete coating of fibers. Thus, such system is more highly preferable from the standpoint of safety including the elimination of potential fire and health hazards arising from the handling of volatile solvents and dry nitrocellulose.

An object of the present invention is to provide a combustible cartridge having a fibrous base containing a multitude of voids or interstitial openings wherein are deposited a mass of crystalline explosive and a method of making the same.

Another object is to provide a process of making a combustible container for munitions having improved physical and chemical properties.

Another object is to provide a fibrous combustible base containing a crystalline explosive for use in the fabrication of a cartridge or case for munitions.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description.

The structure of this invention comprises a fibrous base having a multitude of voids or interstitial openings wherein is deposited a mass of crystalline explosive. In theory, the latter explosive is held in position in the fibrous structure by means of an attraction between differing charges on the fibrous structure and the explosive.

The process of this invention includes the step of dispersing a fibrous base material in an aqueous solution. Subsequently, an additive is added to disperse and condition the fibrous base for the reception of a crystalline explosive which is hereinafter added to the slurry as will be more fully described below. At this point, a binder is added to the slurry to give structural integrity to the item formed from the slurry. The crystalline explosive mentioned above is now added to the slurry in the desired amount. Prior to the addition of the crystalline explosive, it is treated with an electrolyte to condition it for adherence to the fibers of the item. The fibers are now formed into the desired shape and dried to give a combustible item.

In accordance with this invention the chemically degenerated and inherently weak and thermally unstable nitrocellulose of the art is replaced by a high energy, heat resistant and thermally stable crystalline ingredient such as pentaerythritol tetranitrate (PETN), cyclotetramethylene tetranitramine (HMX), cyclotrimethylene trinitramine (RDX), diaminotrinitrobenzene (DATB), and triaminodinitrobenzene (TADB), and 2,4,6-trinitrophenylmethylnitramine (tetryl). When these "crystalline ingredients are incorporated into the cellulosic fibers such as kraft, spun fiber, or filament, they fill the voids between the fibers and enhance the formation of electrical bonds as a result of their particle size and electronic configuration.

In theory, the fibers possess an improved anionic charge induced thereon by sodium carboxymethylcellulose and the crystalline explosive possesses an improved cationic charge induced thereon by means of an electrolytic solution. As a result, the charges are attracted to each other and the explosive is bonded to the fibers at the site of deposition.

Any feltable and combustible fibrous material may be utilized in the construction of the combustible cartridge of this invention. Such fibrous material includes cellulose fibers in the form of kraft or spun filaments, and synthetic fibers such as those of the polyamide or polyester type. The fibrous material should be dispersed in an amount between about 8 and 50 percent, but optimum results have been achieved when 25 percent of fibrous material is utilized in the process. However, if an amount below about 8 percent is used, the final end item will be inherently weak. Also, it has been found that the combustible cartridge will not possess the properties desired if the end item is composed of more than 50 percent of fibrous material.

The additive which is used to disperse and condition the fibrous slurry is sodium carboxymethylcellulose. This material is added to the slurry in order to coat the fibers and thereby give such fibers a propensity for eventual electrical bonding to the crystalline explosive which is subsequently added in the process. Such sodium carboxymethyl cellulose is added to the slurry in an amount between about 2 and 10 percent, but the maximum effect is achieved when it is added in an amount between about 3.5 and 4.4 percent. When an amount below about 2 percent is added, the fibers in the slurry are not uniformly dispersed throughout the slurry, nor is the slurry of sufiicient anionic character to insure the desired amount of electrical bonding between the crystalline explosive and the fibers in the end item. Further, hardly any improvement is achieved in electrical propensity when an amount above 10 percent is utilized in the process.

The binder which is utilized to adhere the fibrous mat as a unit on the mold includes polyamides. This includes the reaction product of polyethyleneimine with dibasic acids such as oxalic acid, maleic acid, malonic acid, adipic acid, and sebacic acid. These products should then be subsequently treated with epichlorohydrin prior to use. The binder prepared as described should be added in an amount between 2 and percent, however, an excellent degree of structural integrity of the fibrous item is achieved when about 12 percent of the binder is utilized in the process. If less than 2 percent of the binder is used to form the item, the adherence of the fibers to each other will be rather weak and the structural integrity of the item will be greatly deminished. However, if an amount greater than 20 percent is used, the combustible nature of the item will be in jeopardy.

The crystalline explosive which is used to form the combustible mat includes PETN, HMX, RDX, DATB and TADB and tetryl. Up to 70 percent of the crystalline explosive may be used to form the combustible item but between about 45 and 70 percent is preferred. Below about 45 percent, the cartridge will not combust as well as desired but above 70 percent, the mat is structurally weak and rather dangerous to handle.

The crystalline explosives listed above should be coated with a water dispersible cationic material such as derivatives of acrylonitride or polyvinyl pyrrolidone. The use of these materials tend toward the establishment of additional bond strength between the cellulose molecule, which is anionic, and the crystalline explosive which is cationic in character. The coatings, although only utilized in the process in small amounts, is sufiicient to decrease the impact sensitivity of the crystalline explosive and this is accomplished by an improvement of the heat stability of the item. These water dispersible cationic materials may be considered as acting as pacifiers by satisfying electrical charges known to exist at the surfaces of these high energy nitrated additives. Such additives should be used in an amount between about 2 and 10 percent by weight based on the weight of the crystalline explosive.

The pH of the process may be maintained between about 5 and 6 during processing in order to facilitate improved bonding between the fibers, which have been conditioned with an anionic charge by sodium carboxymethylcellulose, and the crystalline explosive, which has been coated with a cationic charge-inducing electrolyte.

The following are examples of the process by means of which the improved combustible cartridge or cases of this invention have been prepared.

EXAMPLE I (A) 3.6 lbs. of kraft cellulose having a freeness of 20 was dispersed in 22.5 gallons of water contained in a tank equipped with a variable speed stirrer. Sodium carboxymethylcellulose, in the amount of 0.45 lb., was added to the slurry as a 5 percent aqueous solution. Subsequently, 0.45 lb. of a binder resin of the polyamide type in the form of a 10 percent aqueous solution was added to the slurry and the slurry was maintained under agitation for 20 minutes.

(B) 5 lbs. of PETN having a particle size between 5 and 10 microns was added to 12 gallons of water in a separate tank. Subsequently, 0.25 lb. of sodium carboxycellulose as a 5 percent aqueous solution was added to the explosive slurry. Continuous agitation was maintained and then 0.25 lb. of a polyamide binder as a 10 percent solution was added to the explosive slurry.

(C) The explosive slurry was agitated for 5 minutes, at which time, it was poured into slurry of procedure A., and agitation was continued for 20 minutes.

(D) A cartridge of this invention was then formed by dipping a mold under vacuum into the tank. After the felted cartridge was formed on the mold, it was forced free by reverse pressurization. Subsequently, the formed cartridge was then lifted from the tank and dried at F. for 8 hours.

EXAMPLE II In this example, all parts by weight based on the weight of the entire composition.

(A) 2.5 parts of kraft cellulose was added to 15 gallons of water contained in a 50 gallon tank equipped with a variable speed stirrer for continuous agitation. Subsequently, 1.2 parts of a 10 percent aqueous solution of a polyamide binder was then added to the slurry. The binder in this case was the reaction product of ethylenediamine with adipic acid and epichlorohydrin.

(B) To a separate tank containing 12 gallons of water was added 4.5 parts of RDX and 0.44 part of sodium carboxymethylcellulose. The mixture was agitated for 10 minutes and then 0.58 part of polyvinyl acrylonitrile in the form of a 20 percent aqueous solution was added together with 1 part of polyvinyl pyrrolidone. Agitation was continued for an additional 10 minutes.

(C) The slurry from procedure (B) was then added to the slurry of procedure (A) and agitation was continued for 20 minutes. At the end of this period of agitation, the fibers were ready for mating.

(D) A mold was introduced into the slurry and vacuum was applied. Once the container was formed, it was removed from the mold by reverse pressurization. The formed cartridge was then retrieved from the tank and allowed to dry by standing for 8 hours at 120 F.

The following table illustrates examples of the formulations utilized to form the cartridge cases of this invention by the process heretofore described in Examples I and II. The physical and chemical properties of the finished case are compared to the conventionally available nitrocellulose based items.

TABLE I.-COMPARISON OF FORMULATIONS CONTAIN ING PETN AND NITROCELLULOSE Nominal composition Percentage PETN 55 7O NO 55 70 Kraft 20 20 20 15 Binders 2 25 10 10 Tensile strength, psi. 3, 651 827 1, 610 366 120 Residue, (mg./g.) 28 150 6 45 Impact sensitivity, in 11 10 9 8 8 Heat of explosion, (caL/g.) 520 600 580 562 612 Steel and fiber shoe- Neg. Neg. Neg. Neg. Neg. 134.5 C. heat test, m1

Salmon pink 115 45 105 45 45 Red fumes." 150 75 130 75 75 l Nitrocellulose.

2 Polyethyleneimine derivatives of sebacie acid and. epichlorohydrin.

As noted above, the high mechanical strength and improved thermal stability of the case or cartridge are found in fibrous type containing crystalline explosives such as PETN. As shown, this can be realized without impairing the ignitability of combustibility of the system.

The following illustrates various formulations which have been found to be useful in preparing the product of this invention by the process heretofore described in Examples I and II. The formulations are accompanied by the physical properties of the product of each formulation.

TABLE II.OOMPARISON OF FORMULATIONS CONTAIN- ING VARIOUS HIGH ENERGY ADDITIVES Nominal composition Percentage 5. 8 7. 2 Carboxymethylcellulose (CMC) 4. Tensile strength, p.s.i 2,770 2, 150 2, 740 Residue, mg./g 95 228 182 312 Heat of explosion, cal./g 628 557 571 514 Impact sensitivity 17 9 12 26 1 Poryethyleneimine derivatives of maleie acid and ethylene oxide. 2 Polyvinyl acrylonitrile. 3 Polyvinyl pyrrolidone.

In the fabrication of cartridges or cases to operate under gun firing conditions of up to 40,000 psi, PETN is to be preferred because the excess oxygen available in this molecule is of assistance in. the combustion of the inert portion of the case. Other ingredients such as RDX, HMX, and tetryl are to be preferred in the cartridge or case is intended for use at higher temperature. However, if the cartridge case is intended for use at both higher temperature and pressure, DATB and TADB should be used. The quantities of the above materials may be easily adjusted so as to attain the desired physical properties of the product.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described.

I claim:

1. In a combustible container having a fibrous base con taining a multitude of voids, the improvement of a crystalline explosive positioned and securely adhered in said voids by electrostatic forces, said crystalline explosive being selected from the group consisting of pentaerythritol tetranitrate, cyclotetramethylene tetuanitramine, cyclotrimethylene trinitramine, diaminotrinitrobenzene, triaminodinitrobenzene and 2,4,6-trinitrophenylmethylnitramine.

2. The product of claim 1 wherein said crystalline explosive is pentaerythritol tetranitrate.

3. The product of claim 1 wherein said crystalline explosive is cyclotetramethylene tetranitramine.

4. The product of claim 1 wherein said crystalline explosive is cyclotrimethylene trinitramine.

5. The product of claim 1 wherein said crystalline explosive is diaminotrinitrobenzene.

6. The product of claim 1 wherein said crystalline explosive is triaminodinitrobenzene.

7. The product of claim 1 wherein said crystalline explosive is 2,4,6-trinitrophenyhnethylnitramine.

8. In a combustible container having a fibrous base containing a multitude of voids, the improvement of a crystalline explosive positioned and securely adhered in said voids by electrostatic forces, said crystalline explosive selected from the group consisting of pentaerythritol tetranitrate, cyclotetramethylene tet'anitramine, cyclotrimethylene trinitramine, diaminotrinitrobenzene, tri aminodinitrobenzene and 2,4,6-trinitrophenylmethylnitramine, said explosive present in an amount between about one and about seventy percent by weight based on the weight of said container.

9. The product of claim 8 wherein said crystalline explosive is pentaerythritol tetranitrate.

10. The product of claim 8 wherein said crystalline explosive is cyclotetramethylene tetranitramine.

11. The product of claim 8 wherein said crystalline explosive is cyclotrimethylene tetranitramine.

12. The product of claim 8 wherein said crystalline explosive is diaminotrinitrobenzene.

13. The product of claim 8 wherein said crystalline explosive is triaminodinitrobenzene.

14. The product of claim 8 wherein said crystalline explosive is 2,4,6-trinitrophenylmethylnitramine.

15. In a combustible container having a fibrous base containing a multitude of voids, the improvement of a crystalline explosive positioned and securely adhered in said voids by electrostatic forces, said crystalline explosive selected from the group consisting of pentaerythritol tetranitrate, cyclotetramethylene tetranitramine, cyclotrimethylene trinitramine, diaminotrinitrobenzene, triaminodinitrobenzene and 2,4,6-trinitrophenylmethylnitramine, said explosive present in an amount between about fortyfive to about seventy percent by weight based on the weight of said container.

16. The product of claim 15 wherein said crystalline explosive is pentaerythritol tetranitrate.

17. The product of claim 15 wherein said crystalline explosive is cyclotetramethylene tetranitramine.

18. The product of claim 15 wherein said crystalline explosive is cyclotrimethylene trinitramine.

19. The product of claim 15 wherein said crystalline explosive is diaminotrinitrobenzene.

20. The product of claim 15 wherein said crystalline explosive is triaminodinitrobenzene.

21. The product of claim 15 wherein said crystalline explosive is 2,4,6-trinitrophenylmethylnitramine.

22. The process of making a combustible container comprising dispersing a fibrous base in water,

adding a dispersing and anionic charge-including agent to said dispersion,

admixing a water dispersible binder to said dispersion,

subsequently adding a dispersion of a crystalline explosive to said admixture,

then forming a combustible container from said admixture, and

removing water from said formed item.

23. The process of claim 22 wherein said crystalline explosive is treated with a water dispersible catonic charge-inducing polymer prior to addition to said admixture.

24. The process of making a combustible container comprising,

dispersing a fibrous cellulosic base in water,

adding sodium carboxymethylcellulose in a amount between 2 and 10 percent by weight,

admixing a Water dispersible polyarnide type resin in said dispersion in an amount between 2 and 20 percent by weight,

subsequently adding a crystalline explosive to said ad- 7 8 mixture in an amount of up to 70 percent by weight, 3,260,203 7/1966 Godfrey et al 1492 X said crystalline explosive previously coated with 21 3,264,993 8/1966 De Fries et a1 1492 X water dispersible cationic polymer, 3,280,746 10/ 1966 Brown 149-2 X then forming a combustible container from said ad- 3,371,606 3/1968 Cook et a1. 10224 mixture, and 3,397,637 8/1968 Bobinski et a1. 10238 drying said item in air at 120 F. 5

CARL D. QUARFORTH, Primary Examiner References Cited S. J. LECHERT, JR., Assistant Examiner UNITED STATES PATENTS 694,294 2/1902 Maxim.

10 US. Cl. X.R. 1,498,323 6/1924 Cour 149 2 X 105 

